Brown wire coming through firewall

[jbharkjr]

What are these wires coming through the firewall on the passenger side, rear corner of block, for? Specifically the brown wire by itself. There's one brown wire going to the clip which isn't plugged into anything and then there's a loose brown wire (going down in the picture). Trying to figure out what the loose one is for / goes to.

It's a 1986 Chevy C10.